In a multiple-cylinder engine equipped in a conventional motorcycle, typically, angles of crank angles at which expansion strokes of respective cylinders occur are set to equal intervals. A torque transmitted from the engine to a drive wheel is high in the expansion stroke in the engine and is low in other strokes (intake, compression, and exhaust). In an engine configured to expand at equal intervals, the torque in the expansion stroke is generated at equal intervals and fluctuates regularly. In the engine configured to expand at equal intervals, when the torque of the drive wheel exceeds a slip limit value with respect to a ground surface for a moment in an expansion stroke, a high torque in a next expansion stroke is generated before a gripping force with respect to the ground surface is restored, because an interval before occurrence of the next expansion stroke is short. In this situation, a slip may occur.
Accordingly, an engine has been proposed, in which expansion strokes of respective cylinders of the multiple-cylinder engine are generated at unequal intervals by, for example, arranging crank pins corresponding to the cylinders at unequal angles (see Japanese Patent Application Publication No. 3656921). As shown in FIG. 35, in the engine configured to expand at unequal intervals, an expansion pause interval with a large angle interval is provided in an interval of a crank angle (rotational phase angle of a crankshaft) of expansion strokes (region where the torque increases in FIG. 35) occurring successively. So, the expansion pause interval in which a low torque continues for a long time exists in the engine configured to expand at unequal intervals. Therefore, even if the drive wheel exceeds a slip limit with respect to a ground surface for a moment in the expansion stroke in which the generated torque is high, the gripping force of the drive wheel with respect to the ground surface is restored in the expansion pause interval. That is, by making timings when the high torque is generated irregular, traction performance of the drive wheel is improved.